1. Field of the Invention
The present invention relates generally to electrical power supply distribution, and more particularly to a high voltage distribution system for a radiographic sensor device such as a solid state gamma radiation imaging detector.
2. Description of the Background Art
Radiographic imaging is the detection of radiation from a distributed radiation field in order to form an image. By detecting the amount of radiation emanating from a test subject, the resultant image may give a representative view of the structure of the test subject.
Radiographic imaging typically employs gamma rays. Gamma rays are a form of radiation that is emitted by excited atomic nuclei during the process of passing to a lower excitation state. Gamma radiation is commonly used for medical imaging, and is capable of passing through soft tissue and bone. Gamma radiation may be provided by a radiopharmaceutical, such as thallium or technetium, for example, that is administered to the patient. The radiopharmaceutical travels through the patient's body and may be chosen to be absorbed or retained by an organ of interest. The radiopharmaceutical generates a predictable emission of gamma rays through the patient's body that can be detected and used to create an image.
A radiographic imaging device may be used to detect radiation emanating from the patient and may be used to form an image or images for viewing and diagnosis. Conventional gamma cameras utilize a scintillation crystal (usually made of sodium iodide) which absorbs the gamma photon emissions and emits light photons (or light events) in response to the gamma absorption. An array of photodetectors, such as photomultiplier tubes, is positioned adjacent to the crystal. The photomultiplier tubes receive the light photons from the crystal and produce electrical signals having amplitudes corresponding to the amount of light photons received. The electrical signals from the photomultiplier tubes are applied to position computing circuitry, wherein the location of the light event is determined, and the event location is then stored in a memory, from which an image of the radiation field can be displayed or printed.
Also known in the art are solid-state nuclear imaging cameras, see, e.g., U.S. Pat. Nos. 4,292,645 and 5,132,542. Such cameras use solid-state or semiconductor detector arrays in place of the scintillation crystal and photomultiplier tubes. In a solid-state camera, gamma rays are absorbed in a semiconductor material, creating electron-hole pairs in the semiconductor material. A bias voltage across the semiconductor detector causes the electrons and holes to form an electric current through the semiconductor material. The currents are converted by associated circuitry into electrical signals, which are processed to determine the location and magnitude of the gamma ray absorption event. While solid-state cameras offer potential benefits over the conventional scintillation crystal cameras in terms of reduced weight, improved resolution, improved uniformity, and increased imaging area, the use of such cameras has presented its own set of problems. In particular, early solid-state detectors made of germanium had to be cryogenically cooled to achieve acceptable performance.
Semiconductor detectors made of cadmium zinc telluride (CZT) have recently been proposed for use in solid-state gamma cameras. Such detectors may be operated at room temperature.
A number of radiographic sensor device modules may be tiled in an array to form a detector head. The detector head may be formed such that the radiographic sensor modules are individually detachable for maintenance, adjustment, etc.
The electrical signals generated by each component radiographic sensor device must be communicated to a processor or other device for interpretation, manipulation, and storage. Therefore, each radiographic sensor device must include a wiring harness to communicate the electrical signals to a processor of some sort. For the sensor array, the electrical connection is typically done through a pin grid array, having an array of pins corresponding to the sensor elements. However, the sensor elements generally output low voltages and are fairly simple to connect.
The electrical power supply provided to a cathode of each radiographic sensor device is typically a high negative voltage. The high voltage supplied to the cathode is used to control the current induced in the semiconductor material as a result of gamma interaction. Typically, the electrical power has been provided in the prior art by simple wire or trace connections, such as for example, a metal cathode substrate layer formed on the detector and connected to an electrical supply by wires or cables.
In the prior art the electrical power supply connection to the cathode has been problematic. The electrical power voltage level may be relatively high. Therefore, the prior art conductor connecting the cathode to an electrical power supply must be relatively large. In addition, for purposes of maintenance and repair, it is desirable that individual radiographic sensor devices be capable of being disconnected and reconnected without the necessity of disassembling the entire detector array. It is imperative that this be accomplished without compromising the electrical connection. Therefore, the electrical power supply path must be capable of self-alignment and a guaranteed contact.
What is needed, therefore, are improvements in high voltage distribution for solid-state radiographic detector devices.